The present invention relates to a selector device for a semiconductor wafer with respect to the type of electroconductivity of the wafer, which utilizes the dependency of the polarity of the electromotive force produced in the wafer by the wafer's Hall effect on the conductivity type.
Most of the prior art selector devices for this purpose utilize either the (a) the point-contact rectifier probe method or (b) the thermoelectromotive force method by the use of probes. The results obtained by the use of the former method are frequently from erroneous, especially, for semiconductor wafers with relatively low resistivity. The use of the latter method is characterized by a lengthy time required to perform the measurement, especially when used with semiconductor wafers with relatively high resistivity.
Thus, it is a general practice in the semiconductor technology to use the selector devices of either the former type or the latter type in accordance with the resistivity of the semiconductor wafer undergoing measurement. It is, of course, very troublesome in routine measurement work to switch the selector devices as the resistivity range of the wafer under measurement differs from one wafer to another, leading, consequently, to frequent errors in the determination of the type of surface electroconductivity, which is a problem that is common for both types of devices.
An alternative method for the determination of the conductivity type in a semiconductor wafer material which utilizes the principle that the polarity of the electromotive force produced in a semiconductor wafer by the Hall effect depends upon the type, i.e. n type or p type, of the electroconductivity of the wafer. Although this method has some advantages in that the conductivity type of the semiconductor wafer can be determined reliably regardless of the surface conditions and resistivity of the wafers, it is very difficult to design a practical and reliable selector device utilizing this principle due to the necessity of strong magnetic fields to produce a sufficient electromotive force by the Hall effect, which can be achieved only by the use of a large electromagnet. Further, even with a very large and strong electromagnet, the Hall effect method frequently gives erroneous results in the determination of the conductivity type for a reason that is not well understood.